Sizing an Exhaust Fan

The following data should help you in determining the CFM capacity of a fan for a specific room. The values are easy to calculate. There are minimum standards to follow. Here is where they are put to use. Let's take a small kitchen for an example. Say the kitchen measures 10 feet by 12 feet with an eight foot ceiling. That computes to 960 cubic feet of air in the room. The minimum requirements say that this air should be changed 15 times an hour. This means that a fan must have the ability to move 14,400 cubic feet of air in an hour. Since there are 60 minutes in an hour, we must divide the 14,400 by 60 to get CFM (cubic feet per minute). Cubic feet of 14,400 per hour divided by 60 equals 240 CFM. Nothing to it! Table Values courtesy of Nutone, Inc.

The room area is listed in square feet. All values below the listed room size represent the fan's minimum capacity shown in cubic feet per minute.